The Zuiyō Maru carcass: a 'plesiosaur' in the nets off Christchurch (1977)

The Zuiyō Maru belonged to the Taiyō Fishery Co. Ltd. In April 1977 it was trawling for mackerel about 30 miles east of Christchurch, New Zealand. Aboard were Captain Akira Tanaka, assistant production manager Michihiko Yano, 39, and about 17 other crew.

April 25, 1977. Something became entangled in the nets at a depth of about 300 meters. It was drawn toward the ship and hoisted above the deck. Then it slipped from its ropes and fell suddenly onto the deck.

Yano's first verdict was blunt. "It's a rotten whale!" he told the captain. But as he got a better look, he became less sure. Some of the crew thought of a giant turtle with its shell peeled off. They nicknamed it "Nessie."

What lay on deck was about 10 m long and an estimated 1,800 kg. A small head on a long neck. Four large reddish fins, no lower jaw, no organs. A white, sticky, fat-like substance covered much of it, over red muscle. It was slimy and foul-smelling, like a dead marine mammal.

Yano measured it and took five photographs on a borrowed camera. He kept 42 pieces of horny fibre from a front fin. After about an hour, the corpse was thrown overboard to avoid spoiling the fish catch. It sank back into its watery grave.

Yano returned to Japan on 10 June 1977. About two months after the catch he drew a sketch. On 20 July the story made front pages in Japan, the same day as the company's press conference. Taiyō Fishery sent its boats to find the carcass, apparently without success.

A plesiosaur craze followed. Toys, an advertising campaign, fishing boats heading to New Zealand. On 2 November 1977 Japan issued a commemorative stamp. Yoshinori Imaizumi of the Tokyo National Science Museum called it a plesiosaur-like reptile. Tokio Shikama of Yokohama National University said it "has to be a plesiosaurus."

A scientific team met twice in September 1977, and in July 1978 the Société Franco-Japonaise d'Océanographie published nine papers, edited by Tadayoshi Sasaki, president of Tokyo University of Fisheries. Kimura and colleagues found elastoidin in the fin fibres, a collagen known only from sharks and rays, and its amino-acid profile matched the basking shark. Seta identified the white coating as adipocere, the waxy substance fat turns into as a body decays. Obata and Tomoda objected to the shark, but found no known fossil reptile that fit. The joint conclusion: not certain, but most likely a basking shark or a close relative.

A rotting basking shark loses its jaws, gill arches, dorsal fin and tail fin first, and what remains can look like a small head on a long neck. Glen Kuban later counted only six or seven neck vertebrae, far fewer than a plesiosaur, and pointed to an apparent dorsal fin in one photograph. Western scientists suggested a sea lion, a small whale or a leatherback turtle. Creationist writers cited the case for years. In New Zealand, a museum curator noted that such finds "always turns out to be a basking shark, or an adolescent whale."

The carcass is gone. Five photographs, a sketch and the fin samples remain. The creature lives on in Arthur C. Clarke's Mysterious World, in Godzilla vs. King Ghidorah and in Tekken: The Motion Picture. A dead animal that refused to stay buried.